The role of lung biopsy for diagnosis and prognosis of interstitial lung disease in systemic sclerosis: a systematic literature review

Background The prognostic and theragnostic role of histopathological subsets in systemic sclerosis interstitial lung disease (SSc-ILD) have been largely neglected due to the paucity of treatment options and the risks associated with surgical lung biopsy. The novel drugs for the treatment of ILDs and the availability of transbronchial cryobiopsy provide a new clinical scenario making lung biopsy more feasible and a pivotal guide for treatment. The aim of our study was to investigate the usefulness of lung biopsy in SSc ILD with a systematic literature review (SLR). Methods PubMed, Embase and Cochrane databases were searched up to June 30, 2023. Search terms included both database-specific controlled vocabulary terms and free-text terms relating to lung biopsy and SSc-ILD diagnostic and prognosis. The SLR was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA). Studies were selected according to the PEO (population, exposure, and outcomes) framework and Quality assessment of diagnostic accuracy studies (QUADAS) were reported. Results We selected 14 articles (comprising 364 SSc-ILD patients). The paucity and heterogeneity of the studies prevented a systematic analysis. Diffuse cutaneous SSc was present in 30–100% of cases. Female predominance was observed in all studies (ranging from 64 to 100%). Mean age ranged from 42 to 64 years. Mean FVC was 73.98 (+/-17.3), mean DLCO was 59.49 (+/-16.1). Anti-Scl70 antibodies positivity was detected in 33% of cases (range: 0-69.6). All patients underwent surgical lung biopsies, and multiple lobes were biopsied in a minority of studies (4/14). Poor HRCT-pathologic correlation was reported with HRCT-NSIP showing histopathologic UIP in up to 1/3 of cases. Limited data suggest that SSc-UIP patients may have a worse prognosis and response to immunosuppressive treatment compared to other histopathologic patterns. Conclusions The data from this SLR clearly show the paucity and heterogeneity of the studies reporting lung biopsy in SSc ILD. Moreover, they highlight the need for further research to address whether the lung biopsy can be helpful to refine prognostic prediction and guide therapeutic choices. Supplementary Information The online version contains supplementary material available at 10.1186/s12931-024-02725-1.

High resolution computed tomography (HRCT) is the imaging gold standard to confirm the presence of ILD in SSc and is considered a sensitive and reproducible method for quantifying the extent of ILD, although radiomics may be more sensitive than visual analysis to capture features indicating SSc-ILD severity on HRCT [7,8].However, the radiologic and pathologic correlations between HRCT and lung biopsy features of SSc-ILD remain poorly investigated.The most relevant radiologic pattern observed in SSc-ILD is non-specific interstitial pneumonia (NSIP), but recent studies suggest that among SSc-ILD with late stage disease usual interstitial pneumonia (UIP) is the predominant pattern (87% of cases) and detailed pathologic studies in the early phase of the disease are lacking [9][10][11].
In SSc-ILD patients, lung biopsy is mainly performed when there is a discrepancy between clinical manifestations and HRCT findings and when other diseases, that may complicate SSc clinical course (e.g.lymphomas, lung carcinoma), must be excluded [9].In selected cases, lung biopsy in combination with BAL may rule out infections, aspiration, and drug toxicity.However, the prognostic role of histopathological subsets and the utility of lung biopsy in guiding the therapeutic strategy in SSc-ILD has been largely neglected [9,12].Also the influence of coexistent connective tissue diseases (CTDs) potentially influencing the HRCT and lung biopsy results has also not been properly explored to date.The clinical approach to SSc-ILD contrasts with that of idiopathic interstitial pneumonias (IIPs) where robust data have shown that lung biopsy findings are pivotal in the diagnosis and prediction of prognosis.In fact, histopathological UIP is associated with a worse survival in comparison with other pathological patterns of lung injury [13,14].This different diagnostic approach between IIPs and SSc-ILD is due mainly due to: (1) the lack of effective treatment of ILD in SSc, (resulting in the use of clinical features for diagnosis and treatment choices), and (2) the risks and costs associated with the surgical lung biopsy that have discouraged its use in SSc ILD.However, the development of novel drugs for the treatment of UIP/IPF and progressive fibrotic lung disease, and the availability of transbronchial cryobiopsy provide for a new scenario [6,15].Moreover, the availability of tissue from cryobiopsy may significantly improve the understanding of SSc-ILD and the consequent management of these patients [9,[15][16][17].
Therefore, we have investigated, through a systematic literature review (SLR) of the available literature, the role of lung biopsy in the management of SSc patients in order to assess its utility either for both clinical practice and research purposes.

Methodology and quality assessment
The SLR was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA).Studies were selected according to the PEO (population, exposure, and outcomes) framework outlined in supplementary data S1 (Data S1).Quality assessment of diagnostic accuracy studies (QUADAS) for articles included in the systematic review is summarize in supplementary table S2 (Table S2).

Literature search strategy
PubMed, Embase and Cochrane databases were queried for any relevant publications.Each database was searched from its inception date until June 30th, 2023.Search terms included both database-specific controlled vocabulary terms and free-text terms relating to lung biopsy and SSc-ILD diagnosis and prognosis.Pubmed and Cochrane were interrogated for "biopsy AND (scleroderma OR systemic sclerosis) AND interstitial lung disease AND (diagnosis OR diagnostic OR prognosis OR prognostic)".Embase was questioned for ' biopsy:ti,ab AND (scleroderma:ti,ab OR 'systemic sclerosis':ti,ab) AND 'interstitial lung disease':ti,ab AND diagnos*:ti,ab OR ('biopsy'/exp AND 'scleroderma'/exp AND 'interstitial lung disease'/exp AND ('diagnosis' OR 'diagnostic procedure')).
between lung biopsy (all types) and SSc-ILD.Case reports, reviews, congress abstracts, letters to editor and editorials were excluded as well as case series with less than 10 SSc patients.Moreover, studies in which chest CT was not done were excluded.A detailed flow chart describing the study inclusion and exclusion process is available in Fig. 1.

Data extraction
All identified articles were imported into Mendeley for screening.After deduplication, two screening rounds were performed, as described in Fig. 1.Firstly, two reviewers (A.D and F.F) separately evaluated titles and abstracts in terms of relevance for both biopsy and SSc-ILD.In the second round, full texts of the included articles were re-checked for eligibility.In case of disagreement during selection a third reviewer (S.BR) was consulted and a consensus reached.
The extracted contents were as follows: (1) The basic characteristics of the included studies: name of the first author, publication year, location of the studies, study design; study duration (months), total number of included patients, total number of SSc patients in the study, number of control population if present, SSc definition criteria (ACR 2013 criteria, ARA 1980 criteria); (2) other data: percentage of limited and diffuse cutaneous SSc, percentage of female patients, mean age (years), availability of PFTs, FVC (% pred) mean and SD, DLCO (% pred) mean and SD, prevalence of ILDs pattern by CT, biopsy technique (trans-bronchial, cryobiopsy, VATS biopsy, open surgical biopsy), prevalence of ILDs patterns on histopathology, availability and duration of follow up.Any biopsy findings on cellularity, cytokines and molecules expression data, previous or current treatments, autoantibodies, and procedure-related adverse events were also examined.

Statistical analysis
Data for continuous variables are summarized as mean +/standard deviation (median, minimum and maximum for not normally distributed variables); data for categorical variable are summarized as prevalence, with number and percentages.To compare mortality of UIP-SSc versus NSIP-SSc we pooled the Fisher's study 5years survival, approximated using Kaplan-Meiers curve, with the Bouros's study reported 5years survival [18,19].

Literature search results
The initial search retrieved 933 results from MED-LINE, 473 from Pubmed, 453 from Embase and 7 from Cochrane Collection through June 30, 2023.In Fig. 1, the flow-chart with details on the included and excluded papers are shown.After removal of duplicates, 878 papers were uploaded into Mendeley.First-stage screening by reviewing titles and abstracts excluded 861 Fig. 1 Flow-chart with details on the included and excluded papers Legend.BAL: Broncho-Alveolar Lavage; ILD: interstitial lung disease; SSc: Systemic Sclerosis publications for not addressing both lung biopsy and SSc-ILD; 17 articles were identified as relevant and assessed for eligibility.After the second-stage screening, 4 articles were excluded because they were not pertinent to the research item.To capture other potentially relevant articles, we also evaluated the full list of references from Reviews, which lead to manual inclusion of 1 additional article which was found to be pertinent to the research item.Finally, 14 articles met all the inclusion criteria constituting the final pool of this SLR (Fig. 1).

Characteristics of the enrolled studies
Characteristics of the included studies are summarized in Table 1.The 14 studies selected in this systematic literature review included 364 SSc-ILD patients.The majority of studies (9/14) were retrospective single center studies.11 studies based SSc diagnosis on ARA 1980 criteria, whereas two studies used the ACR 2013 diagnostic criteria [20,21].In 7 of the included studies, follow up data were available, with a mean duration of 5 years (+/-4.44).

Clinical characteristics and lung function
Diffuse cutaneous SSc was variably present in the cohorts, ranging from 30 to 100% of cases.Female predominance was observed in all studies, ranging from 64 to 100%.Mean age in the studies ranged from 42 years to 64 years.Pulmonary function tests (PFTs) were available in all studies except one by Felicio et al. [22] Mean FVC was 73.98 (+/-17.3),mean DLCO was 59.49 (+/-16.1).PFTs value from Yamakawa et al. were not included in the analysis because of lack of separate data for patients with SSc [23].

Previous or current treatments
In the included studies, previous treatment was poorly characterized.All patients in De Carvalho et al. study [31] (N = 18) and 20/25 patients from Xiao et al. [24], were naïve to treatment.The only previous treatments mentioned were corticosteroids (CCS, 5 patients) and cyclophosphamide (CYC, 3 patients).Five out of 14 studies provided information on ongoing treatment at the time of biopsy and the most common drugs used were CYC and CCS [18,22,26,28,29].
Few studies provided information on guidelines for surgical biopsy.The majority of studies highlighted the importance of avoiding CT honeycombing areas, e one study specified only that two or three biopsy specimens per patient were sampled [31] and in four studies, samples were taken in more than one lobe. 28 33 26None of the studies mentioned adverse events related to the biopsy procedure.
The presence of CLF (interstitial fibrosis centered on membranous and respiratory bronchioles associated to foreign matter in the lumen due to microaspiration) was assessed in two studies only [28,35] showed that CLF was present as an isolated finding in 21% of patients, while some focal regions of this pattern were also found in 84% of patients with predominant NSIP [35].

Radiologic-pathologic correlations
The 4 studies reporting radiologic-pathologic correlations in 73 patients are summarized in Table 2.
Harrison et al. (year of publication 1991) showed that SSc patients without apparent CT changes can have pathologic findings on biopsy: 8 upper or middle lobe biopsies from regions defined as normal by CT were found to have not otherwise specified fibrosis histologically.In 21 cases, CT and histology were concordant in detecting ILDs and 3 normal lungs.In all 3 cases negative both at CT and histology electron microscopy could detect early changes [33].
De Souza evaluated HRCT features of patients with CLF and described that centrilobular or airway centered and patchy distribution of the lung involvement were features of CLF patients, while patients with histological NSIP showed peripheral and more diffuse distribution of ground-glass at HRCT: CLF was always associated with coexisting esophageal dilation (> 4 cm diameter) and with a higher frequency of centrilobular nodules (83%) [35].

Cellular findings on histopathology
Biopsy cellularity was examined in a few studies, either on bronchial mucosal biopsies or lung samples.In 23 patients, Sehlstedt et al. evaluated endobronchial biopsies and reported a higher number of neutrophils [27].In lung biopsies, Harrison et al. evaluated neutrophils, eosinophils, macrophages, lymphocytes, and lymphoid aggregates in o the alveolar spaces and interstitium (determining inflammation): plasma cells were found in the interstitium and lymphoid aggregates and germinal centers were adjacent to bronchioles [33].In lung biopsies, Yamakawa et al. found plasma cells infiltrate, lymphoid aggregates, germinal centers and fibroblastic foci, both in patients with SSc-ILD and ILD patients with SSc antibodies but without other clinical features of SSc [23].6) this study didn't define histopthologic patterns but described all cases as mixed fibrosis and inflammation similar to cryptogenic fibrosing alveolitis, nowadays defined idiopathic pulmonary fibrosis

Molecular findings on histopathology
In 4 studies, data on gene expression, cytokines and other molecular findings in lung or endobronchial biopsies were reported [27].In mucosal endobronchial biopsies, Sehlstedt et al. found a lower epithelial IL-8 and NFkB expression in SSc-ILD samples compared to controls [27].Christmann et al. compared gene expression of macrophage markers, chemokines, collagen, as well as transforming growth factor β-and interferon (IFN)-regulated genes, in lung biopsies of SSc-NSIP and controls.They found that expression of these genes correlated with progressive lung fibrosis defined by progression in radiological score (FibMax).Immunohistochemistry confirmed increased markers of collagen (COL1A1), IFN (OAS1 and IFI44), and macrophages (CCL18 and CD163).Moreover, several genes correlated with both the change in Fib-Max and the change in % predicted forced vital capacity, including IFN and macrophage markers, chemokines, and heat-shock proteins [28].Parra et al. evaluated different expression of proteins regulating NO synthesis, and found that higher levels of iNOS, IL-13 and bFGF expression in lung biopsies of SSc patients with cellular and fibrotic NSIP correlated with the amount of parenchymal fibrosis [30].More recently Xiao et al. evaluated 25 lung biopsies in SSc-ILD and found that the hedgehog pathway activation was increased in the lung tissue of SSc-ILD patients and this was decreased by pirfenidone, Sufu (suppressor of fused) was upregulated in lung fibroblasts after pirfenidone challenge, and pirfenidone inhibited the phosphorylation of GSK-3b signalling [24].
Two prognostic studies compared CTD-ILD to idiopathic NSIP (iNSIP) and there was no mortality difference [22,31].Felicio et al. compared 20 iNSIP to 21 CTD-NSIP (10 were SSc-NSIP) confirming the overall good prognosis of NSIP in both groups (overall survival 135 months for iNSIP and 227 months for CTD-NSIP) [22].De Carvalho et al. compared 22 iNSIP to 18 SSc-NSIP (all fibrotic) finding a higher collagen and elastic fibers content in the SSc-NSIP group, but without prognostic differences on univariate Kaplan Meyer analysis [31].

Disease progression
In 3 studies the functional decline of SSc-ILD was evaluated (Table 3) [18,26,35].Only Kim et al. compared the functional decline between NSIP and UIP, reporting a better outcome after immunosuppressive treatment for NSIP compared to UIP (15% FVC improvement in 5/12 NSIP cases treated with CCS and CYC, compared to no improvement in the 5 UIP patients and a decrease in the CRP score after treatment only in the NSIP group) [26].Only De Souza compared functional decline between NSIP and CLE without finding any statistically significant difference [35].

Discussion
This systematic review on the utility of lung biopsy in SSc ILD clearly highlights the need for further research on this topic.Over the last 20 years, only a limited number of studies have employed lung biopsy either in the evaluation and management of patients with SSc-ILD or in order to better understand the pathophysiology of SSc.The present review highlightss the paucity and heterogeneity of the studies in terms of population selection, study aims and data collection.These limitations do not permit a systematic analysis and no solid conclusions on the role of biopsy in SSc-ILD diagnosis and management can be drawn.
Acknowledging those limitations, the most interesting finding of this SLR is that definition of histopathological pattern in SSc-ILD may have a prognostic and therapeutic significance.Only the Fisher study was sufficiently powered to detect a statistically significant difference in mortality among subgroups, providing very low quality evidence that in SSc-ILD UIP pattern may correlate with a higher mortality and a worse response to immunosuppressive treatment compared to NSIP [19,26].This finding is well established in IIPs and in rheumatoid arthritis related ILD (RA-ILD) [36].The PANTHER trial has clearly shown that in UIP/IPF immunosuppression is detrimental and more recently the TRAIL-1 trial has shown that pirfenidone significantly slows lung function decline only in RA-ILD with UIP pattern but not with other patterns [37,38].Without further studies these findings cannot be extended to SSc-ILD where UIP pattern may have a different prognostic and theragnostic implications.The Park et al. study was excluded from the present SLR because of the absence of SSc-ILD population data [39].However, it is important to underline that those Authors found a higher survival rate in CTD-ILD patients compared to IIPs, with CTD-UIP having a better prognosis compared to IPF-UIP, thus suggesting a possible different pathobiological background and prognosis for UIP related to SSc compared to its idiopathic counterpart [39].In this systematic review, only one study compared the prognosis of cellular and fibrotic NSIP, but it failed to find a meaningful difference [18].This is strikingly divergent from what is known in IIPs and in other ILDs, where a cellular NSIP has a better prognosis and treatment response compared to fibrotic NSIP [40].The clinical significance of histopathologic findings in SSc-ILD may also vary over time and among patient subsets.SSc-ILD histopathologic features of the overall population at baseline may differ from those of progressive SSc-ILD.In progressive fibrotic SSc-ILD the prevalence and clinical impact of histopathologic UIP remain completely unexplored.Neither the SENSCIS, nor the INBUILD trial were designed according to histopathology data, therefore the real impact of molecular or morphological histopathological features on treatment response remains unexplored and lung biopsy role for SSc-ILD patients management continues to be neglected [41,42].The paucity of data reviewed in this SLR underline the urgent need to explore the universe of SSc-ILD patterns and pathobiological prognostic factors.
In SSc-ILD the UIP-HRCT pattern is rarely found, as it was seen in 13% of cases according to our review.In fact, this SLR confirmed that NSIP-HRCT is be the most prevalent pattern in SSc-related ILD (75%).However, there are limitations to consider.First of all, the majority of the studies predate the 2011 IPF guidelines that defined the diagnostic categories of the fibrotic patterns on HRCT.Moreover, several studies may have had selection bias including a priori only NSIP-SSc, excluding those studies the prevalence of NSIP-HRCT is 61.3%.The studies reviewed in this SLR show that HRCT-pathologic pattern correlation is imprecise.Histological UIP pattern may be present in up to one third of radiological fibrotic NSIP [19].
Among the other histopathologic patterns described in this review, CLF has been explored in 2 studies, with an overall prevalence of 9.8% in SSc-ILD.This pattern seems to correlate with chronic aspiration, a common complication of SSc, and does not seem, with very limited data, to have a meaningful prognostic impact.Given the paucity of studies and the high risk of bias no firm conclusion can be drawn.Moreover, PPFE and unclassifiable ILD, introduced 10 years ago in the histological classification [40], have been reported only in a few studies, and thus remain to be further explored [23].Radiological PPFE was reported by Enomoto et al. to occur in 19% of patients with CTD-ILD (in 43% of patients with SSc-ILD), and PPFE-like HRCT lesions increased significantly the risk of death for respiratory causes (hazard ratio: 4.10, 95% confidence interval: 1.33-12.65,p = 0.01) [43].In SSc, Bonifazi et al. have shown the important negative prognostic impact of radiological PPFE, but its biological mechanisms are to be further elucidated [23,44].
The lung biopsy techniques reported in this SRL are obsolete and therefore we may advocate for future studies relying on more innovative and safer biopsy approaches such as transbronchial cryobiopsy [45].The number of segments and lobes biopsied is incompletely reported and in many studies only one lobe was biopsied, introducing a risk of potential bias due to discordance of histopathologic features known to occur in different lobes [46].Future studies should investigate optimal site(s) for lung biopsy using HRCT or more sophisticated guiding systems to allow precise radiologic-pathologic correlations [47].Cryobiopsy performed in experienced centers for the diagnosis of ILDs is safe [45].However, the safety data in SSc-ILD are limited.Both the lung function impairment and the possible vascular involvement should be carefully considered in SSc-ILD patients.There are no absolute contraindications to biopsy, but the indication for lung biopsy in patients with pulmonary hypertension or poor lung function should be very carefully balanced against the increased risk of possible severe complications.
Most of the included studies in this SLR were performed before the clinical use of antifibrotic therapies which now provide a much more extensive therapeutic armamentarium: different histopathologic patterns may predict different responses to drugs.In SSc-ILD, Xiao et al. showed the efficacy of pirfenidone as an antifibrotic compound in SSc fibrosis-related pathways [24].In SSc patients, Parra et al. pointed out the importance of selectively inhibit inducible Nytric Oxyde Synthetasis pathway to avoid reperfusion damage during vasodilators treatments, suggesting the need of further study to understand the mechanisms of action of available drugs and to develop new therapies [30].Novel transcriptomics technique are emerging and the importance of a lung tissue biobank is of critical importance for future development of targeted treatments [48].There is an urgent unmet need to define histopathological findings in SSc-ILD.Unlike for the idiopathic ILDs, in SSc the real prevalence and significance of NSIP and UIP histopathological patterns remain largely unclear.Understanding whether these morphological patterns have therapeutic or prognostic significance is of major importance.molecular characterization of diseased lung may become part of the future landscape of precision treatment and may supercede morphologic classification and the UIP/NSIP dichotomy.In either case cryobiopsy remains a relatively safe biopsy alternative for traditional histopathologic evaluation and for tissue procurement for molecular studies.
In conclusion, the data obtained from this SLR suggest that lung biopsy does provide discriminating data characterizing pulmonary involvement in SSc patients.Future studies are needed to address whether it can be helpful to either refine our prognostic prediction or to guide treatment.

Table 1
. Christmann et al. evidenced the presence of CLF in 5/ 21 patients, whereas the other 16 patients presented a NSIP pattern [28].De Characteristics of the enrolled studies Souza et al.

Table 2
SSc-ILD, radiologic and histopathologic features and correlations

Table 3
Prognostic significance of histopathology findings in SSc-ILD